This invention relates to a method and apparatus for shaping the distal surfaces of a human femur, employing a novel adjustable shaping guide, which is fixed to an intramedullary alignment guide which aligns with the central long axis of the femur. The invention has particular applicability to surgery in which only a single condyle, either the medial or lateral condyle, is replaced with a unicondylar prosthesis.
In replacing a knee joint which has been damaged due to disease or trauma, it is very important that the prosthesis used to replace the damaged portion of the joint be properly aligned with respect to the bone to which the prosthesis is fixed. Particular problems are encountered when replacement of only one condyle with a unicondylar prosthesis is required, in that most femoral shaping instrumentation relys on aligning with respect to the cortical aspect of the anterior condyle whereas in most replacements of only a single condyle it is the distal and posterior condyles that should be referenced for alignment. Alignment using the unaffected side of the femur as a reference point does not facilitate ease and accuracy in aligning such prostheses. This difficulty is due to the poor visability of the unaffected posterior condyle resulting from soft tissue obstruction and limited surgical exposure.
To enable a surgeon to shape the distal femur to receive a femoral component of a total knee joint prosthesis, Leo A. Whiteside, one of the named inventors herein, developed a method and apparatus for shaping a distal femoral surface which is claimed in U.S. Pat. No. 4,474,177 (issued 10/2/1984). That '177 Patent is hereby incorporated by reference to teach the use of an intramedullary alignment guide which provides the surgeon with a means for determining the central long axis of the femur and a means by which the surgeon can shape the distal femur relative to that axis by attaching distal femoral shaping instruments to that
alignment guide. The '177 Patent teaches the use of a number of shaping guides to accomplish the shaping of the distal femoral surfaces. A more detailed surgical procedure describing this method of shaping the distal femur is described in Brochure No. L095-0201 9/85 entitled "Whiteside ORTHOLOC (TM) Total Knee System" from Dow Corning Wright, Arlington, Tenn. (1985). Specific examples of two such shaping guide instruments described in that brochure (A/P Bevel Cutting Guide and Distal Cutting Guide) are shown in Brochure No. L095-PN003 entitled "New Whiteside ORTHOLOC (TM) Total Knee Instruments" also by Dow Corning Wright. This type of cutting guide may be used in conjuction with the guide of the present invention to obtain correct rotational alignment and for distal condyle resection immediately prior to use of the guide of this invention.
The shaping guide instruments described in the above patent and brochure lock onto the handle of the alignment guide and take their alignment from the position of the alignment guide handle. The distal cutting guide disclosed in the last mentioned brochure includes a sighting bar for rotational alignment. The purpose of this bar is to assure that the intramedullary rod is positioned in the proper rotational alignment for the particular knee being worked on. Brochure No. 86-038-5780-0525/16MA (1986) from Zimmer, Inc., Warsaw, Ind., entitled "ZIMMER (R) Intramedullary Knee Instrumentation For the Miller Galante Total Knee System" shows an Anterior Femoral Cutting Guide Instrument No. 5785-018 which uses a locator to reference the anterior femoral cortical surface and thus guide resection of the anterior aspects of the femoral condyles relative to that anterior cortical surface. That Guide Instrument is mounted on a Femoral IM (intramedullary) Alignment Guide No. 5785-012. However, the other distal femoral surfaces are then shaped after the IM Alignment Guide is removed from the femur and several different shaping guides are employed to accomplish the shaping of the femur.
U.S. Pat. No. 4,722,330 issued to Russell and Whiteside teaches the use of a feeler gauge which references the anterior femoral cortical surface to locate a femoral surface shaping guide which is similarly mounted on an intramedullary rod.